Ethernet switching is provided to interconnect multiple Ethernets for the exchange of Ethernet data frames. Most Ethernet switches require data buffering and Ethernet signal regeneration at the switch which incur the problems of substantial signal processing, power consumption, and transmission delay. In copending U.S. patent application Ser. No. 12/148,708, the teachings which are incorporated by reference, we extended the carrier sensing multiple accessing of Ethernet to route through a Multi-stage Interconnection Network (MIN). The invention described in Ser. No. 12/148,708 relieves these problems by allowing Ethernet signals to pass through a multistage interconnection network with fast control and minimum processing and delay, thereby producing a switch that consumes substantially less power. At each stage of the network, carrier sensing is performed in the transmission path. Carrier sensing is performed step-by-step and in-band until an end-to-end transmission path is found.
The present invention described herein provides a new out-of-band control method for an Ethernet switch that solves the same problems.
In conventional Carrier Sense Multiple Access with Collision Detection (CSMA/CD), a communication node first senses if a carrier is present in the transmission medium. If the medium is sensed busy, then the attempt to transmit is delayed. If the medium is sensed idle, then the transmission proceeds immediately. However, it is possible that two nodes sensing an idle medium may transmit simultaneously, resulting in a transmission collision. With Collision Detection (CD) by each transmitting node, transmission is aborted and a random time delay is introduced for each node to attempt transmission again via the CSMA/CD protocol.
An alternative Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) employs a handshake procedure instead. The transmitting node issues a Request-to-Send (RTS) signal and must receive back a Clear-to-Send (CTS) signal from the intended receiving node before beginning a transmission. The handshake serves as a notification to all other nodes to refrain from transmitting, thus avoiding collisions. This extension to the CSMA protocol is primarily intended for use with wireless transmission media where CSMA/CD would not work because it is not possible for a node to listen and detect a collision while transmitting.
Both CSMA/CD and CSMA/CA utilize timing (temporal switching) of the transmission to avoid collision. A third technique that utilizes spatial switching to avoid collision in disclosed in U.S. patent application Ser. No. 12/148,708 which extended the CSMA/CD protocol to sense presence or absence of a carrier at random times in a single medium. Through Carrier Sense Multiple Access in Time-Space (CSMA/TS), carrier sensing is performed step-by-step for multiple links in a path and is possible over alternative paths. Hence, carrier sensing is performed not only in time, but also in the space of multiple links and multiple paths.
Carrier sensing for data rate beyond Gigabit per second (Gb/s) speed is difficult technically, and hence is not practiced for 10 GB/s Ethernet. The difficulty comes from two reasons: first, at high data rate, propagation delay relative to packet transmission time becomes significant and second, carrier sensing of a transmission medium may disturb signal fidelity. The present invention employs CSMA/TS using a unique and innovative out-of-band control network for media access and routing. Instead of carrier sensing and collision detection/avoidance, the invention advantageously takes the approach of sending explicit RTS and CTS messages through an out-of-band multi-stage network.
Route control of Multi-stage Interconnection Networks (MIN) is difficult to perform in parallel and fast. Switches built using MN are typically controlled by centralized Stored Program Control (SPC). Route establishment is often performed sequentially and therefore does not scale well with increasing traffic and switch size.
One aspect of the invention, instead of using SPC for routing, employs a separate control plane with parallelism. The invention discloses new and parallel routing and contention resolution mechanisms for an aggregate switch throughput in tens of Terabits per second on a frame by frame basis.
Having a separate control plane also facilitates more connectivity functions which we include in this patent application. The disclosed switch can control connectivity flexibly. Connectivity can be made frame by frame, or semi-permanently such as in establishing Virtual Local Area Network (VLAN). The disclosed switch can provide connectivity not only for Ethernets but also for other interfaces including Small Computer Standard Interface (SCSI) and Peripheral Computer Interface (PCI or serialized PCI called PCI Express). This architecture is hereafter referred to as Carrier Sensed Integrated Switching (CSIS).